My engine slows down after about a minute or so running at near top speed on the bench. I'm using a masterscrew 7x6 propeller. Is the pitch too much for the engine?

probably not excessive ptich.. I use 7X6 on my .09's don't lean it for peak rpm... open the needle about 3 clicks from where you get top rpm. Any engine will overheat durring bench runs if you have it too lean.

First, running your engine too hot is not good for it. I think your engine is not yet broken in, or you are using a fuel with too little oil, or both. As far as props go, I'm not familiar with your engine. I saw an LA 10 run on an APC 7 x 5 today and was not impressed. I advised going to a 7 x 4, but they did not put up another flight so I can't say how it came out. My experience has been with TD 09's which I have run a lot and tried a bunch of different props on. The Cox 7 x 3.5 has been the best. When I run out of those, I'm going to try a 7 x 3 APC. I would think an OS 10 would be happy turning some RPM's , but that's just a guess, I suppose.

Jim

If you are still using the fuel you mentioned in the thread below, that is probably your problem. The fuel said NOT to use it in airplane engines...well! (You might want to point that out to your hobby dealer.)
The problem is that some car fuels use very small amounts of lube. This works well in car engines because they are turning very high RPM with comparatively light loads...and many are BB.
You have an airplane engine running at 1/3 the RPM with a much higher load.
I don't know if you understand about sleeve bearings but when the shaft turns in a bearing, the lube builds up pressure that trys to suspend and even center the shaft in the sleeve. This applies to the crankshaft and the connecting rod in your engine. The faster the shaft turns, the more the pressure buildup. HOWEVER, the smaller the amount of lubricant, the less the pressure. When the RPM or the amount of lubricant is insufficient, the metals rub together and wear.
This also applies to the piston/cylinder but it works a little differently.
I would suggest switching to an airplane fuel with 15% nitro, 22% castor lube,and using a 7x3 or 7x4 prop (as Jim mentioned) for your glider.
Note that some RC type airplane fuel is formulated for large BB, ABC engines that do not need as much lube as you do. Check the lube content.

George

Well, thank you all for your coments and recommandations. I will try different props. The fuel I'm using now is power-master 15% nitro and 18% castor /synthetic. I used a quart of fuel for RC cars before I noticed It wasn't for airplanes engines.

I have an OS max 10 in an airplane that has well over a hundred flights on it. I flew it several times yesterday. I use a master airscrew 8-4, which performs very well on this airplane. It will idle down so that you can almost see the prop turning, and with 2 ¼ inch diameter wheels it takes off from a grass strip. I have used both Omega 10%nitro and Red Max 15% nitro fuel. The glow plug is a Fox with idle bar. I suspect you are running it a little lean. I always adjust just a little rich of peak RPM, and have had no trouble with either overheating, or cutting out at idle. A seven inch diameter propeller will certainly let the engine rev a little higher, however the thrust will not necessarily be more. Be patient breaking it in and you will have a great little engine that will give you years of service.